外文翻譯空調(diào)與制冷技術(shù)

1、附錄附錄A 外文翻譯Air Conditioning and Refrigeration TechnologyAir conditioning has rapidly grown over the past 50 years, from a luxury to astandard system includedin most residential and commercial buildings. In 1970, 36% of residences in the U.S. were either fullyair conditioned or utilized a room aircond

2、itioner for cooling (Blue, et al., 1979). By 1997, this numberhad more thandoubled to 77%, and that year also marked the first time that over half (50.9%)ofresidences in the U.S. had central air conditioners (Census Bureau, 1999). Anestimated 83% of all newhomes constructed in 1998 had central air c

3、onditioners(Census Bureau, 1999). Air conditioning has alsogrown rapidly in commercialbuildings. From 1970 to 1995, the percentage of commercial buildings withairconditioning increased from 54 to 73%.Air conditioning in buildings is usually accomplished with the use of mechanicalor heat-activatedequ

4、ipment. In most applications, the air conditioner must providebothcoolinganddehumidificationtomaintaincomfortinthebuilding.conditioning systems are also used in other applications, suchas automobiles, trucks, aircraft, ships, and industrial facilities. However, the description of equipment inthis ch

5、apter is limited to those commonly used in commercial and residential buildings.Commercial buildings range from large high-rise office buildings to the corner convenience store.Because of the range in size and types of buildings in thecommercial sector, there is a wide variety ofequipment applied in

6、 these buildings. Forlarger buildings, the air conditioning equipment is part of atotal system design thatincludesitemssuchasapipingsystem,airdistributionsystem,andcoolingtower.Proper design of these systems requires a qualified engineer. The residentialbuildingsectorisdominatedbysinglefamilyhomesan

7、dlow-riseapartments/condominiums. The cooling equipment applied in thesebuildings comes instandard“packages”thatareoftenbothsizedandinstalledbytheairconditioningcontractor.Thechapterstartswithageneraldiscussionofthevaporcompressionrefrigeration cycle then movesto refrigerants and their selection. Ch

8、illers and their auxiliary systems are then covered, followed bypackaged air conditioning equipment.Even though there is a large range in sizes and variety of air conditioningsystems used in buildings, mostsystems utilize the vapor compression cycle to produce the desired cooling and dehumidificatio

9、n. Thiscycle is also used for refrigerating and freezing foods and for automotive air conditioning. The first patenton a mechanically driven refrigeration system was issued to Jacob Perkins in 1834 inLondon, and the firstviable commercial system was produced in 1857 by James Harrison and D.E. Siebe

10、(Thevenot 1979).Besides vapor compression, there are two less common methods used to producecooling in buildings:the absorption cycle and evaporative cooling. These are described later in the chapter. With the vaporcompression cycle, a working fluid, which is called the refrigerant, evaporates and c

11、ondenses at suitablepressures for practical equipment designs.The four basic componentsin every vapor compression refrigeration systemare thecompressor, condenser, expansion device, and evaporator. The compressorraisesthepressureoftherefrigerantvaporsothattherefrigeranttemperature is slightly above

12、the temperature of thecooling medium used in thecondenser. The type of compressor used depends on the application of thesystem.Large electric chillers typicallyuse a centrifugal compressor while small residential equipmentuses a reciprocating or scroll compressor.The condenser is a heatexchanger use

13、d to reject heat from the refrigerant to a coolingmedium.Therefrigerantentersthecondenserandusuallyleavesassubcooled liquid. Typical cooling mediums usedin condensers are air and water. Mostresidential-sized equipment uses air as the cooling medium in thecondenser, whilemany larger chillers use wate

14、r.After leaving the condenser, the liquid refrigerantexpands to a lower pressure in the expansion valve.The expansion valve can be a passive device, such as a capillary tube or short tube orifice, or an activedevice, such as a thermal expansion valve or electronicexpansion valve. The purpose of the

15、valve is toregulate the flow of refrigerant to the evaporator so that the refrigerant is superheated when it reachesthe suction of thecompressor.At the exit of the expansion valve, the refrigerant is at a temperature below that of the medium (air orwater) to be cooled. The refrigerant travels throug

16、h a heatexchanger called the evaporator. It absorbsenergy from the air or water circulatedthrough the evaporator. If air is circulated through the evaporator,the system is called a direct expansion system. If water is circulated through the evaporator, it isachiller. In either case, the refrigerant

17、does not make direct contact with the air or water in the evaporator.The refrigerant is converted from a low quality, two-phase fluid to a superheated vapor under normaloperating conditions in the evaporator. The vapor formed must be removed by the compressor at asufficient rate to maintain the low

18、pressure in the evaporator and keep the cycle operating.All mechanical cooling results in the production of heat energy that must berejected through thecondenser. In many instances, this heat energy is rejected to the environment directly to the air in thecondenser or indirectly to water where it is

19、rejected in a cooling tower. With some applications, it ispossible to utilize this waste heat energy to provide simultaneous heating to the building. Recovery ofthis wasteheatat temperatures up to 65C (150F) can be usedto reduce costs for space heating.Capacities of air conditioning are often expres

20、sed in either tons or kilowatts (kW)of cooling. The tonis a unit of measure related to the ability of an ice plant to freeze one short ton (907 kg) of ice in 24 hr.Its value is 3.51 kW (12,000 Btu/hr). The kW of thermal cooling capacity produced by the air conditionermust notbe confused with the amo

21、unt of electrical power (also expressed in kW) required to producethe cooling effect.Refrigerants Use and SelectionUp until the mid-1980s, refrigerant selection was not an issue in most building airconditioningapplicationsbecausetherewerenoregulationsontheuseofrefrigerants. Many of the refrigerants

22、historicallyused for building air conditioningapplicationshavebeenchlorofluorocarbons(CFCs)hydrochlorofluorocarbons(HCFCs).Mostoftheserefrigerantsarenontoxicnonflammable. However,recent U.S. federal regulations (EPA 1993a; EPA 1993b)and international agreements (UNEP, 1987) haveplaced restrictions o

23、n the production and use of CFCs and HCFCs. Hydrofluorocarbons (HFCs) are nowbeing used in someapplicationswhereCFCsandHCFCswereused.Havinganunderstandingofrefrigerants can help a building owner or engineer make a more informed decision about the best choiceof refrigerants for specific applications.

24、 This section discussesthe different refrigerants used in or proposedfor building air conditioning applications and the regulations affecting their use.The American Society of Heating, Refrigerating and Air Conditioning Engineers(ASHRAE) has astandard numbering system (Table 4.2.1) for identifying r

25、efrigerants (ASHRAE, 1992). Many popularCFC, HCFC, and HFC refrigerants are in the methane and ethane series of refrigerants. They are calledhalocarbons, or halogenated hydrocarbons, because of the presence of halogen elements such as fluorineorchlorine (King, 1986).Zeotropes and azeotropes are mixt

26、ures of two or more different refrigerants. A zeotropic mixture changessaturation temperatures as it evaporates (or condenses) atconstantpressure.Thephenomenaiscalledtemperatureglide.Atpressure, R-407C has aboiling (bubble) point of44C (47F) and acondensation(dew) point of 37C (35F), which gives it

27、a temperature glide of 7 C (12F). Anazeotropicmixture behaves like a single componentrefrigerant in that the saturationtemperature does not changeappreciably as it evaporates or condenses at constantpressure. R-410A has a small enough temperatureglide (less than 5.5 C, 10F) that itis considered a ne

28、ar-azeotropic refrigerant mixture.ASHRAE groups refrigerants (Table 4.2.2) by their toxicity and flammability(ASHRAE, 1994).Group A1 is nonflammable and least toxic, while Group B3 is flammable and most toxic. Toxicity isbased on the upper safety limit for airborne exposure to the refrigerant. If th

29、e refrigerant is nontoxicin quantities less than 400 parts per million, it is a Class A refrigerant. If exposure to less than 400 partsper million is toxic, then the substance is given the B designation. The numerical designations referto the flammability of the refrigerant. The last column of Table

30、4.2.1 shows the toxicity and flammabilityrating of common refrigerants.Refrigerant 22 is an HCFC, is used in many of the same applications, and is still the refrigerant ofchoice in many reciprocating and screw chillers as well as smallcommercial and residential packagedequipment. It operates at a mu

31、ch higher pressure than either R-11 or R-12. Restrictions on the productionof HCFCs will start in 2004.In 2010, R-22 cannot be used in new air conditioning equipment. R-22cannot beproduced after 2020 (EPA, 1993b).R-407CandR-410AarebothmixturesofHFCs.Bothareconsideredreplacements for R-22. R-407Cis e

32、xpected to be a drop-in replacement refrigerant for R-22. Its evaporating and condensing pressuresfor air conditioning applications areclose to those of R-22 (Table 4.2.3). However, replacement of R-22with R-407Cshouldbedoneonlyafterconsultingwiththeequipmentmanufacturer.Ataminimum,the lubricant and

33、 expansion device will need to be replaced. The firstresidential-sized air conditioningequipment using R-410A was introduced in the U.S. in 1998. Systems using R-410A operate at approximately50% higher pressure thanR-22 (Table 4.2.3); thus, R-410A cannot be used as a drop-in refrigerantfor R-22.R-41

34、0A systems utilize compressors, expansion valves, and heat exchangers designedspecificallyfor use with that refrigerant.Ammonia is widely used in industrial refrigeration applications and in ammoniawater absorptionchillers. It is moderately flammable and has a class B toxicity ratingbut has had limi

35、ted applications incommercial buildings unless the chiller plant can beisolated from the building being cooled (Toth, 1994,Stoecker, 1994). As a refrigerant, ammonia has many desirable qualities. It has a high specific heat andhigh thermalconductivity. Its enthalpy of vaporization is typically 6 to

36、8 times higher than that of thecommonly used halocarbons, and it provides higher heat transfer compared tohalocarbons. It can beused in both reciprocating and centrifugal compressors.Research is underway to investigate the use of natural refrigerants, such ascarbon dioxide (R-744)and hydrocarbons in

37、 air conditioning and refrigeration systems(Bullock, 1997, and Kramer, 1991).Carbon dioxide operates at much higher pressures than conventional HCFCs or HFCs and requiresoperation above the critical point in typical air conditioning applications. Hydrocarbon refrigerants,often thought of as too haza

38、rdous because of flammability, can be used in conventional compressors andhavebeen used in industrial applications. R-290, propane, has operating pressures close to R-22 and hasbeen proposed as a replacement for R-22 (Kramer, 1991). Currently,there are no commercial systemssold in the U.S. for build

39、ing operations that use eithercarbon dioxide or flammable refrigerants.From:Composite Index Ashrae Handbook Series空調(diào)與制冷技術(shù)過去501970 36% 的住宅不是全空氣調(diào)節(jié)就是利用一個(gè)房間空調(diào)器冷卻；到1997年，這一數(shù)字達(dá)到了 77%，(人口普查局1999)。在1998年，83%的新建住宅安裝了中央空調(diào) ( 人口普查局, 1970年到1995年，有空調(diào)的商業(yè)建筑物的百分比從54%73%(杰克森和詹森,1978)。建筑物中的空氣調(diào)節(jié)通常是利用機(jī)械設(shè)備或熱交換設(shè)備完成.在大多數(shù)應(yīng)用

40、空調(diào)在商業(yè)和住宅建筑中的應(yīng)用。質(zhì)的工程師才能完成。居住的建筑物(即研究對(duì)象)被劃分成單獨(dú)的家庭或共有式計(jì)尺寸和安裝。擇，然后介紹冷卻設(shè)備及附屬系統(tǒng)，最后介紹組合式空調(diào)機(jī)組。雖然空調(diào)系統(tǒng)應(yīng)用在建筑物中有較大的尺寸和多樣性,大多數(shù)的系統(tǒng)利用蒸1834Perkins的人在倫敦獲得了機(jī)械制冷系統(tǒng)的第一專利權(quán)，在1857Harrison和D.E. Siebe生產(chǎn)出第一個(gè)有活力的商業(yè)系統(tǒng)(Thevenot 1979)，除了蒸汽壓縮循環(huán)之外 , 有兩種不常用的制冷方法在建筑物中被應(yīng)用: 有一種叫制冷劑的工作液體，它能在適當(dāng)?shù)墓に囋O(shè)備設(shè)計(jì)壓力下蒸發(fā)和冷凝。使用一個(gè)離心式的壓縮機(jī)而小的住宅設(shè)備使用的是一種往復(fù)或漩渦式壓縮機(jī)。介質(zhì)。入口的時(shí)候, (空氣或水) 的溫度以下。熱量，如果空氣經(jīng)過蒸發(fā)器在流通,該系統(tǒng)叫做一個(gè)直接膨脹式系統(tǒng)，如果水經(jīng)過蒸發(fā)器在流通,它叫做冷卻設(shè)備，在任何情況下，在蒸發(fā)器中的制冷劑不直接蒸發(fā)器中低壓和保持循環(huán)進(jìn)行。在冷凝器中這個(gè)熱能被直接散發(fā)到環(huán)境的空氣中或間接地散發(fā)到一個(gè)冷卻塔的溫度為65(150F)的廢熱可以減少建筑物中采暖的費(fèi)用。(千瓦)24小時(shí)內(nèi)使1噸 (907 公斤)的水結(jié)冰的能力有關(guān)，其值是3.51千瓦(12,000Btu/hr)，空調(diào)的冷卻能力不要和產(chǎn)生冷量所需的電能